Feast Watson Outdoor Furniture Oil is a good option to protect timber outdoor furniture. It is specifically designed for outdoor furniture.
If you were to use a decking product you might find it leaves staining on clothing as contact with materials shouldn't be a regular occurrence.
Look at a marine grade polyurethane. This will help against the weather but also the amount of tinnies that will be placed upon one's masterpiece.
Spray is the way to go. If you don't have a spray gun, then roll and finish off by using a fine grade brush, similar to using gloss enamel. You will probably need at least three coats, sanding lightly in between." – darylhewston
I don't like varnish as it ends up peeling when exposed to the elements. I would use a natural oil. You could use a decking oil, linseed oil or a specialist product like Osmo or Whittle Waxes exterior oil. These can all be applied with a good brush. You would need 2–3 coats with a light sand in between.
It does need some maintenance, but in my opinion you retain the natural beauty of the timber with oils. There are some very good hard wax oils which do have a gloss finish. The trick is applying multiple thin coats. The oil penetrates the timber and is not just a coating like varnish. " – She_Skills
I suggest having a look at Bondall 1L Gloss Monocel Gold Marine Clear Timber Varnish as an overall sealer for a table. It will provide two very important things to protect your pine table UV protection and moisture contamination. The sun and heavy moisture are the things that will deteriorate your table.
In order for the Bondall 1L Gloss Monocel Gold Marine Clear Timber Varnish to bond properly to the timber surface. It'll be necessary to sand off all the current varnish on the table and chairs. I suggest using an electric sander to make it easier to prepare the table.
This would also be a good opportunity to repair any damage with filler and tighten up the screws of the table. I recommend a minimum of two coats for optimum protection. Here is a handy step-by-step guide: How to restore wooden furniture.
Please remember to wear personal protection such as gloves, goggles and a mask while working on your table. - EricL